by
Arnold Plotnick MS, DVM, ACVIM, ABVP

“He’s looking kinda
thin lately”

Danny, a lovable 12 year old orange male tabby owned by
Stephanie and Andres Lazerus, has an impressive medical
history. Four years ago, he was diagnosed with diabetes.
He was prescribed insulin and his diabetes quickly
responded. Two years later he developed hyperthyroidism,
a common glandular disorder of older cats. Oral
medication was prescribed and his hyperthyroidism
rapidly came under control. A year ago, miraculously,
his diabetes went into complete remission and he no
longer required insulin. Since then he’s been fed a
low-carbohydrate diet, and his blood sugar has remained
normal. Now he was in my exam room because lately,
there’s been a little less of Danny to love.

Upon questioning, it was clear that Danny was doing
fairly well otherwise. His appetite remained good, his
thirst was normal, and there was no reported coughing,
sneezing, vomiting, or diarrhea. On physical
examination, however, he looked like the “after” photo
in an imaginary feline weight loss advertisement. At his
last visit, Danny was a robust 12 pounds. Today, he was
down to 9 ¼ pounds despite his decent appetite. I
recommended an initial battery of blood tests to try to
figure out his cause of the weight loss. “We’ve been
coming here for years. You know how we feel about Danny.
Do whatever tests are necessary”, said Andrew. The hunt
for a diagnosis was on.

Common Causes
There are many potential causes for weight loss in cats.
Decreased food intake is an obvious cause, and poor
appetite is a common concurrent complaint. Poor appetite
and weight loss are general, vague clinical signs,
however, and the list of possible illnesses is
extensive. It narrows considerably when you consider the
age of the cat. In a senior cat like Danny (cats aged 11
to 14 years) (see sidebar on feline life stages), weight
loss is likely due to either a metabolic problem or a
gastrointestinal problem. When a cat experiences weight
loss despite a normal (or even an increased) appetite,
the list of possibilities narrows even further.

The most common metabolic problems that cause weight
loss in a senior cat are diabetes, hyperthyroidism, and
chronic renal failure (CRF). Diabetes is one of the most
common glandular disorders in cats, affecting about 1 in
400 cats in the United States. Diabetes occurs when the
pancreas fails to produce adequate amounts of insulin, a
hormone necessary for controlling blood sugar levels.
Like Danny, most cats diagnosed with diabetes are over
seven years of age, and males are almost twice as likely
to become diabetic as females. Overweight cats are more
likely to be afflicted.

Diabetes is usually easy to diagnose. Most cats present
with the classic signs: excessive urination, excessive
thirst, very good appetite, and weight loss. Danny was
eating normally, but his thirst and urination were
normal as well. Given his history of having had diabetes
in the past, I had to see if he had relapsed. A complete
blood count, chemistry panel, thyroid test and
urinalysis were part of our initial work-up. “Most
diabetics have an elevated blood sugar level, and have
sugar in the urine. These are the first things we look
for when making our diagnosis”, says Dr. Michael Stone,
a veterinary internist at the Cummings School of
Veterinary Medicine at Tufts University. I checked
Danny’s blood and urine. The results were clear: Danny’s
blood sugar was normal, and there was no sugar in his
urine. Danny was not diabetic.

Hyperthyroidism is the most common glandular disorder in
cats. It occurs when the thyroid gland in the cat’s neck
produces an excessive amount of the thyroid hormone
thyroxine (T4). It is seen mainly in senior and
geriatric cats, the average age being around 12 or 13
years. “The most common clinical sign is weight loss”,
notes Dr. Stone. “The next most common sign is ravenous
appetite. A variety of other signs – excessive thirst
and urination, vomiting, diarrhea, increased shedding,
vocalization, restlessness – may or may not be present
as well. “Hyperthyroidism is very treatable. In fact, it
is curable. Hyperthyroid cats can be given an injection
of radioactive iodine under the skin. The iodine travels
to the thyroid gland where it disrupts the function of
the thyroid cells, preventing them from releasing
excessive amounts of T4. The T4 levels return to normal
and the cat is cured. This treatment is safe but
expensive, and can only be done at certain referral
centers. A more common treatment involves administering
the oral medication methimazole. This drug prevents the
thyroid gland from releasing excessive amount of T4 into
the bloodstream. It is not a cure. If the owner stops
administering the drug, the thyroid gland will resume
producing excessive amounts of T4, and the clinical
signs will recur.

Diagnosing hyperthyroidism is usually easily
accomplished by measuring the level of thyroid hormone
in the bloodstream. Interestingly, Danny had been
diagnosed with hyperthyroidism years before and was
receiving his methimazole consistently. “Occasionally, a
cat’s thyroid medication requirements will change, and
some cats require an increase in dosage over time”,
cautions Dr. Stone. Aware of this possibility, I
measured Danny’s T4 level. It was right in the middle of
the normal range. Poorly-controlled hyperthyroidism was
not the cause of Danny’s weight loss.

Chronic renal failure (CRF) is perhaps the most common
cause of weight loss in senior cats. Signs of kidney
disease include increased thirst, excessive urination,
weight loss, and vomiting. Cats with CRF, however, tend
to have a poor appetite compared to diabetic cats and
cats with hyperthyroidism; the latter often have
increased appetite.

Diagnosis of CRF is usually made via blood and urine
tests. The kidneys remove toxins from bloodstream and
put them in the urine. When the kidneys fail, the toxin
level will rise and the urine becomes dilute. Although
Danny wasn’t showing any of the other common signs of
CRF, the disease is such a common cause of weight loss
in older cats that it behooved us to check. But Danny’s
urine was adequately concentrated, and the level of
kidney toxins in his blood stream was in the normal
range. CRF was not the cause of Danny’s weight loss.

Going for the Gut
Having ruled out the familiar metabolic causes of weight
loss in senior cats, I suspected a gastrointestinal (GI)
cause. Two common GI disorders are inflammatory bowel
disease and low-grade gastrointestinal lymphoma.
Inflammatory Bowel Disease (IBD) is an uncontrolled
inflammatory response resulting in the infiltration of
inflammatory cells into parts of the gastrointestinal
tract. Although any age cat can be affected, most cats
are middle aged or older. Not surprisingly, the most
common symptom of feline IBD is weight loss. This may be
accompanied by a decreased appetite, vomiting, or
diarrhea. In most cats, physical examination of the GI
tract tends to be normal, as was the case with Danny.
Occasionally, thickened or fluid-filled intestines are
evident when the abdomen is examined. Routine laboratory
tests tend to be normal.

Gastrointestinal cancer can strike cats of any age,
although it is mostly seen in older cats. The GI tract
is susceptible to several types of cancer, however,
low-grade lymphoma is the most common. The average age
of affected cats is 9 to 13 years. The most common
clinical signs are weight loss and decreased appetite.
Vomiting occurs in about 50% of cases, and diarrhea in
about 30%.

X-rays and ultrasound are common diagnostic procedures
used to diagnose GI disease in cats. X-rays alone,
however, are ineffective for diagnosing IBD or lymphoma.
Increased intestinal wall thickness and enlarged
abdominal lymph nodes may be visible on ultrasound in
suspected cases of IBD and low-grade lymphoma, however
these finding are merely suggestive, not diagnostic.
Ultimately, a definitive diagnosis requires obtaining
biopsy specimens from the GI tract.

Biopsies can be obtained either via endoscopy or
exploratory surgery. Endoscopy is a procedure in which a
long, flexible snake-like tube (the endoscope) enters
the GI tract through the cat’s mouth (“upper GI
endoscopy”) or anus (“lower GI endoscopy”) in order to
visualize the internal lining of the GI tract and obtain
biopsy specimens. Endoscopy is less invasive than
surgery and allows for direct examination of the mucosal
surfaces (innermost lining) of the GI tract. One
limitation of endoscopy is that the biopsy specimens
obtained by this method consist only of the mucosal
lining rather than a full-thickness biopsy of the
intestine, occasionally resulting in a misdiagnosis.
Exploratory surgery allows the procurement of better
biopsy specimens, although surgery is more expensive and
more invasive. Both procedures – endoscopy and abdominal
surgery – require general anesthesia.
Because I felt certain that Danny had a primary GI
disorder, Danny’s owners elected to skip the ultrasound
and proceed right to endoscopy. With no renal failure,
no diabetes, and well-controlled hyperthyroidism, the
anesthetic risk was minimal. Danny was scheduled for
endoscopy the following day.

At endoscopy, the stomach looked normal, but the inner
surface of the intestines had a pale, cobblestone type
of appearance. Multiple biopsy specimens were obtained
and Danny was awakened and sent home that evening. Two
days later, the pathology report arrived. Danny had low
grade intestinal lymphoma.

A Diagnosis and a Dilemma
Understandably, Danny’s owners were distraught upon
hearing the diagnosis. I informed them, however, that
although cancer is often a devastating diagnosis, the
low-grade form of GI lymphoma is one of the more
treatable feline cancers, and most cats show an
excellent response to oral medications. Oral
chemotherapy will not cure the condition, however. The
chemo protocol most commonly prescribed for low-grade GI
lymphoma consists of two drugs, prednisolone (commonly
referred to in conversation as “pred”) and chlorambucil.
The average survival time on these medications is around
25 months. Some cats fare better; others fare much
worse.

Chlorambucil is usually well tolerated, however, a few
cats will experience side effects. The most common
adverse effects are GI toxicity and suppression of the
bone marrow (the marrow is where the body manufactures
red blood cells, white blood cells, and platelets). GI
signs – vomiting, diarrhea, decreased appetite – are
usually mild and resolve on their own.

Prednisolone is a steroid that also has the potential to
cause side effects. Some cats will drink more water and
urinate more when given pred. Others may show an
improved appetite when given pred, which may be of
benefit in those cats in which poor appetite was a major
clinical sign of illness. A few cats, when given pred
twice daily for long periods, become diabetic. This is
where Danny’s dilemma arises. Danny, having been
diabetic before, was at increased risk of becoming
diabetic again if given pred. To avoid this, I chose to
treat with chlorambucil alone and will evaluate whether
he gains weight and goes into remission. If not, I may
add prednisolone to the regimen and monitor closely. If
he becomes diabetic, I may need to stop the drug, or we
may once again need to give him insulin. “I’m glad we
have a diagnosis, and that there’s a treatment”, says
Stephanie. “He’s dealt with hyperthyroidism, and he’s
dealt with diabetes. I’m sure he’ll be able to deal with
this as well”.
I am, too.